Abandoned Phone Cable Buzzes to Life on Ocean Floor / Line being used to monitor quakes and tidal waves

Carl T. Hall, Chronicle Science Writer

Published 4:00 am, Thursday, October 1, 1998

An old telephone cable, left for dead on the bottom of the Pacific Ocean, is humming once again as the computer-driven lifeline of the world's first deep-sea earthquake monitor.

AT&T donated the 35-year-old "Hawaii 2" cable after fiber-optic technology rendered the twisted strands of steel and copper obsolete. It fell into disuse in 1989, after fishing boats had shredded some sections beyond repair.

Now, after 12 years of design and construction work, the cable has been transformed into a 1,000- mile-long power cord and communications link for the new Hawaii 2 Observatory, affectionately known to its builders as "H2O."

The instruments are anchored 16,000 feet below the surface to a novel titanium junction box located 1,200 miles west of the California coast. Besides hookups for incoming power and a data-feed back to Oahu, there are enough connections for eight sets of instruments.

It already serves as Station No. 108 in the Global Seismic Network, used to track earthquakes around the world. Seismologist Rhett Butler, who manages the system for a consortium of 90 research institutions known as IRIS, said the new undersea station patches a gaping hole in what had been an entirely land-based network.

"It's going to make a big difference," he said. "If you are in California and you are interested in earthquakes, as soon as you step off the coast, there's been nothing to monitor what's happening until all the way to Hawaii or Alaska."

The deep-sea seismic instruments offer a new way to take readings while quakes are happening, perhaps leading to detection of previously unknown faults and more accurate predictions of aftershocks.

By gauging ocean currents, the system may also sound early warnings for devastating tsunami waves long before they reach land. All the data is automatically fed over the cable back to a relay system that will soon be connected to the University of Hawaii and eventually made available worldwide via the Internet.

The seagoing work involved bringing the cable to the surface through a difficult series of maneuvers using a remote diving vessel dubbed Jason, a larger version of the vehicle used to explore the wreckage of the Titanic.

Disaster nearly struck when a supporting chain -- rated for 30,000 pounds and holding up just 8,000 pounds -- inexplicably snapped midway through the installation, sending the whole array to the bottom of the ocean. Scientists were able to recover the device undamaged, succeeding after another try.

"It landed upright perfectly," Butler said. "It sort of flew down to the seafloor like a kite."

Project engineers fashioned the junction box entirely of titanium so it could withstand the harsh seafloor. It hooks up instruments that include a broadband seismometer, hydrophones for listening to marine life and detecting the pressure of waves passing above, and devices for tracking local sea currents and temperature.

Scientists hope to install a magnetic sensor to gauge pulses from the Earth's core. Other possibilities include more sophisticated sensors for spying on the deep-sea biology.

A 400-watt power source drives it all from Hawaii. Old-fashioned vacuum tube repeaters every 20 miles -- the original equipment installed by AT&T has never failed -- help keep the information from decaying before it reaches land.

The project was financed in part by a $2.4 million National Science Foundation grant. But getting hold of the old transoceanic cable was the real key.

It was all but worthless in the modern phone system, capable of handling only 138 phone calls at a time, a tiny fraction of the capacity on new digital circuits. But it was more than adequate as a 1,000- mile extension cord to the middle of the Pacific.